Support tube of a camshaft with varying wall thickness

ABSTRACT

A support tube for a camshaft may include at least one setting region for setting at least one component and a free region adjoining the setting region. The support tube may further include a tube wall that has a varying thickness. In the setting region, the tube wall may exhibit a wall thickness that is greater than the wall thickness of the tube wall in the free region. Furthermore, a method for producing such a support tube may involve forming a profiled strip material with varying wall thickness into the support tube. In some cases the tube wall of the support tube may be hydroformed.

The present invention relates to a support tube for a camshaft having avarying tube wall thickness. Furthermore, the invention relates to acamshaft comprising a support tube with a varying tube wall thickness,and to a method for producing said support tube.

PRIOR ART

It is fundamentally known that camshafts, in particular assembledcamshafts serve for the valve control of an internal combustion engine.Assembled camshafts are known for example from DE 3 717 190 C2 withsintered cams or from DE 4 121 951 C1 with forged cams. The cams can bemounted on the carrier shaft or support shaft of the camshaft in a widevariety of ways. Thus, it is possible for the carrier shaft itself to byslightly widened at those axial positions at which the cams are intendedto be fastened, for example by being rolled, wherein subsequently, thecams are pushed over the tube or the carrier shaft as far as theintended axial position. As a result, it is possible to create a formfit and/or force fit between the carrier shaft and the cam. It islikewise known for the cams to be connected to the carrier shaft bywelding. A defined configuration of cams can be found for example in EP1 860 285 A1. Vehicle manufacturers, in particular OEMs, generally wishto provide assembled camshafts with a low weight and high strength. Thisis on account in particular of the increasingly stringent legalrequirements in terms of emission levels of combustion engines. Onepossibility for saving weight is for example to produce cams whichexhibit as small a volume as possible and an associated weight. It isfurthermore conceivable to also produce the support tube itself with areduced material mass, in order to achieve a desired weight reduction orweight optimization. However, in particular in the case of a supporttube for a camshaft, it is necessary, on account of the mountingprocess, in which the individual cams are attached to the support tube,to maintain a particular minimum wall thickness, in particular aparticular wall thickness ratio between the outside diameter and theinside diameter of the support tube.

SUMMARY OF THE INVENTION

Therefore, it is the object of the present invention to provide asupport tube, in particular a camshaft, which is/are producible easilyand cost-effectively, and afford sufficient weight-saving potential and,with regard to the connecting concepts in each case, allow reliable andeconomical mounting of individual components.

The above object is achieved by a support tube for a camshaft having thefeatures of claim 1 and by a camshaft comprising a support tube havingthe features of claim 5 and by a method for producing the support tubehaving the features of claim 10. Further features and details of theinvention can be gathered from the dependent claims, the description andthe drawings. Here, features and details which are described inconjunction with the support tube according to the invention also apply,of course, in conjunction with the camshaft according to the inventionand the method according to the invention, and vice versa in each case,and so reciprocal reference is or can always be made with regard to thedisclosure relating to the individual aspects of the invention.

The support tube according to the invention for a camshaft comprises atleast one setting region for setting at least one component and a freeregion adjoining the setting region, and a tube wall that has a varyingthickness. According to the invention, in the setting region, the tubewall exhibits a wall thickness which is thicker than the wall thicknessof the tube wall in the free region. Advantageously, the support tube isin the form of a hollow shaft and accordingly comprises athrough-opening extending in an axial direction along the support tube.This serves particularly advantageously for the production of alightweight camshaft, in particular of a lightweight support tube. Thesupport tube for the camshaft is consequently a constituent part of anassembled camshaft, which, as described below, comprises, in addition toa support tube, components which are connected to the support tube in aform-fitting and/or force-fitting manner. Setting of the component onthe setting region of the support tube is understood, in the scope ofthe invention, as meaning in particular that the at least one componentis arranged or mounted, advantageously connected in a force-fittingand/or form-fitting manner to the support tube at least in the settingregion. Advantageously, the thickened portion of the wall thickness ofthe tube wall of the support tube extends in the direction of thethrough-opening and consequently into the interior of the support tube.This means that the outer circumferential surface of the support tubeitself is formed in such an unvarying manner that no transition oroffset can be found between the setting region and the free region ofthe support tube.

In the scope of the invention, it is furthermore conceivable for thetube wall to exhibit, in the setting region, a wall thickness whichcorresponds to about 110% to 190% of the wall thickness of the tube wallin the free region. Advantageously, depending on the component to be setor on the setting method used, that is to say with or without thesupport tube being pretreated, the wall thickness of the setting regionvaries with respect to the wall thickness of the tube wall in the freeregion. Thus, it is possible for the support tube to comprise aplurality of setting regions, which each exhibit different wallthicknesses from one another. Consequently, it is possible for settingregions which are pretreated with a raised material formation, such as arolled formation, to exhibit a greater or thicker wall thickness thanfor example a setting region of the support tube that has not besubjected to a pretreatment.

Furthermore, it is possible for the tube wall to exhibit, in the settingregion, a wall thickness which is twice the wall thickness of the tubewall in the free region. Advantageously, it is conceivable here for,even when there are several setting regions, these each to exhibit twicethe wall thickness compared to the free regions formed advantageouslybetween the setting regions. As a result, easy and cost-effectiveproduction of the support tube is possible.

It is moreover conceivable for the support tube to have been produced bymeans of hydroforming. By virtue of the hydroforming, the formation ofdifferent wall thicknesses of setting regions and free regions isadvantageously easily possible. However, it is also conceivable for thesupport tube to have been produced by means of some other process.Accordingly, it is possible for the support tube to have been producedby means of a cold upsetting process or even an upsetting process withapplication of heat. Advantageously, use is made of an upsetting pressfor this purpose. By means of the upsetting process, in particulardefined different wall thicknesses of the support tube are created.

Also claimed is a camshaft which comprises a support tube of theabovementioned type and at least one component set in the setting regionof the support tube. Advantageously, the camshaft comprises a pluralityof set components. In this case, it is conceivable for the camshaft tocomprise for example a setting region on which a plurality of componentsare set. It is also conceivable for the camshaft, in particular thesupport tube of the camshaft, to comprise a plurality of settingregions, wherein each of the setting regions comprises at least one,advantageously a plurality of components.

It is also possible for the component to be a cam, a cam segmentcomprising at least two cams with mutually different cam tracks, abearing ring, a sliding element comprising at least one guide track, ora support sleeve for the arrangement of a cam, of a cam element or of asliding element. Advantageously, the camshaft comprises a plurality ofvery different components. In this case, it is conceivable forcomponents of very different configuration to each be set or arranged ona corresponding separate setting region or on one and the same settingregion. Advantageously, a plurality of components are consequentlyarranged alongside one another in a manner spaced apart from one anotherin an axial direction via a free region or in a manner directlyadjoining one another (in contact with one another) on a setting regionor a plurality of setting regions.

In the scope of the invention, it is furthermore conceivable that, atleast in the setting region, the material of the tube wall of thesupport tube comprises, on its outer circumferential surface, at leastone raised formation or a protrusion or a toothing. The raised formationor raised material formation and the protrusion serve advantageously forpositioning and particularly advantageously for holding or fixing the atleast one component. In this case, it is possible for the component orat least one component to be arranged in a force-fitting manner on thesupport tube. The toothing serves advantageously for the form-fittingarrangement of the at least one component on the support tube, inparticular the setting region of the support tube. It is conceivable forthe camshaft to comprise a support tube which comprises a plurality ofsetting regions, wherein each of the setting regions comprises amutually different outer surface. This means that, for example, one ofthe setting regions can comprise a raised material formation, whileanother of the setting regions has a toothing. Advantageously, theconfiguration of the outer surface of each particular setting region isdependent on the component to be set on the setting region.

It is furthermore possible for the toothing to be a longitudinaltoothing. This has the advantageous result that the component arrangedon the setting region provided with the longitudinal toothing can bemoved at least to some extent in an axial direction.

It is furthermore likewise possible for the raised formation to be arolled formation. A rolled formation is a raised material formation thatis producible in a simple manner and serves for a force-fittingarrangement of a component on the support tube.

The camshaft according to the invention leads to all the advantages thathave already been described for the support tube according to the firstaspect of the invention.

Also claimed is a method for producing an abovementioned support tube ofan abovementioned camshaft, wherein a profiled strip material comprisinga varying wall thickness is formed into the support tube.

The method described leads to all the advantages that have already beendescribed for the support tube according to the first aspect of theinvention and for the camshaft according to the second aspect of theinvention.

A camshaft according to the invention is explained in more detail in thefollowing text with reference to a drawing, in which, schematically:

FIG. 1 shows a sectional illustration from the side of an embodiment ofa camshaft according to the invention with an embodiment of a supporttube according to the invention.

FIG. 1 schematically illustrates a sectional illustration from the sideof an embodiment of a camshaft 10 according to the invention with anembodiment of a support tube 1 according to the invention. Consequently,the camshaft 10 comprises a support tube 1, which is in the form of ahollow shaft. A through-opening 5 extends in an axial direction throughthe support tube 1. The support tube 1 comprises a tube wall 2, whichcomprises at least one setting region 3.1 and 3.2, respectively, and atleast one free region 4.1, 4.2 and 4.3, respectively. Advantageously,the support tube 1 comprises three free regions 4.1, 4.2 and 4.3 and twosetting regions 3.1 and 3.2. In the region of the first setting region3.1, a raised material formation 6 has advantageously been created onthe outer surface 9 of the support tube 1. It is also conceivable for atoothing, in particular a longitudinal toothing, which serves as araised material formation, to have been formed in the first settingregion 3.1.

Furthermore, a cam segment 11 has been set on the support tube 1 in thefirst setting region 3.1. The shaft segment 11 comprises a first cam11.1 and a second cam 11.2. The first cam 11.1 and the second cam 11.2have different cam tracks from one another. In the second setting region3.2 of the support tube 1, a support sleeve 12 has advantageously beenplaced on the support tube 1. Advantageously, no pretreatment of theouter surface 9 of the support tube 1 in the form of a raised materialformation, in particular of a toothing or rolled formation or the like,is formed on the outer surface 9 of the support tube 1 in the secondsetting region 3.2, such that, for example, the support sleeve 12 hasbeen merely slid onto the support tube 1, in particular onto the settingregion 3.2. In this case, it is conceivable for the support sleeve 12 tobe heated, for example, with the result that it undergoes a widening ofits through-bore, such that, after being heated, the support sleeve 12is slid onto the support tube 1 as far as its defined setting region3.2. After the support sleeve 12 has been positioned on the support tube1, the support sleeve 12 is cooled and reaches its starting temperature,with the result that in particular the through-opening of the supportsleeve 12 contracts again and an interference fit between the supportsleeve 12 and the support tube 1 arises. However, alternatively oradditionally to the heating of the support sleeve 12, it would also beconceivable for the support tube 1 to be cooled, at least before thesupport sleeve 12 is slid onto the support tube 1. Advantageously,throughout the sliding-on process, at least the support sleeve 12 isheated or the support tube 1 is cooled. After the support sleeve 12 hasbeen slid onto the support tube 1, at least the support sleeve 12 isthen cooled or the support tube 1 is then heated. This (shaft/hub)connection is also referred to as a thermal shrink fit or thermaltransverse interference fit. Advantageously, in this case, the supportsleeve 12 only covers the support tube 1 in the setting region 3.2 ofthe support sleeve 12 on the support tube 1. Instead of the supportsleeve 12, it also possible for other components, for example a cam or acam segment, a sliding element, etc., to be attached to the support tube1 by means of the abovementioned method.

However, it is also conceivable for a raised material formation forexample in the form of a rolled formation to have been created on theouter surface 9 of the support tube 1 in the second setting region 3.2,such that when the support sleeve 12 is attached to the second settingregion 3.2, a force-fitting connection is allowed on account of thematerial displacement between the support sleeve 12 and the support tube1. The cam segment 11 and the support sleeve 12 are components 20 whichare arranged or have been set on the respective setting regions 3.1 and3.2 of the support tube 1 in order to form a camshaft 10.

As is apparent from FIG. 1, the thickened portions of the wallthicknesses, in particular the wall thickness 8 of the setting regions3.1 and 3.2, extend in the direction of the through-opening 5 and thusinto the interior of the support tube 1. The wall thickness 7 of thefree region 4.1, 4.2, 4.3 is, as is apparent from FIG. 1, less orthinner than the wall thickness 8 of the setting regions 3.1 and 3.2.

LIST OF REFERENCE SIGNS

1 Support tube

2 Tube wall

3.1 (First) setting region

3.2 (Second) setting region

4.1 (First) free region

4.2 (Second) free region

4.3 (Third) free region

5 Through-opening

6 Raised (material) formation

7 Wall thickness of the free region

8 Wall thickness of the setting region

9 Outer surface of the support tube

10 Camshaft

11 Cam segment

11.1 First cam

11.2 Second cam

12 Support sleeve

20 Component

1-10. (canceled)
 11. A support tube for a camshaft comprising: a firstsetting region for setting a first component; a second setting regionfor setting a second component, wherein the first and second settingregions have mutually different outer surfaces; a free region adjoiningthe first and second setting regions; and a tube wall that has a varyingthickness, wherein thickened portions of the tube wall in the first andsecond setting regions have a greater thickness than a thickness of thetube wall in the free region, wherein the thickened portions of the tubewall in the first and second setting regions extend into an interior ofthe support tube such that an outer circumferential surface of thesupport tube is unvarying in that transitions or offsets between thefree region and the setting regions are avoided.
 12. The support tube ofclaim 11 wherein the thickened portions of the tube wall in the firstand second setting regions are 110% to 190% as thick as the thickness ofthe tube wall in the free region.
 13. The support tube of claim 11wherein the thickened portions of the tube wall in the first and secondsetting regions are twice as thick as the thickness of the tube wall inthe free region.
 14. The support tube of claim 11 wherein the tube wallis hydroformed.
 15. The support tube of claim 11 comprising the firstcomponent set on the first setting region, wherein the first componentis at least one of a cam, a cam segment comprising at least two camswith mutually different cam tracks, a bearing ring, a sliding elementhaving at least one guide track, or a support sleeve for receiving a camof a cam segment or of a sliding element.
 16. The support tube of claim11 wherein at least in the first setting region a material of the tubewall has on the outer circumferential surface at least one of a raisedformation, a protrusion, or a toothing.
 17. The support tube of claim 16wherein the toothing is a longitudinal toothing.
 18. The support tube ofclaim 16 wherein the raised formation is a rolled formation.
 19. Amethod for producing the support tube of claim 11, the method comprisingforming a profiled strip material that has a varying wall thickness intothe support tube of claim
 11. 20. A support tube for a camshaftcomprising: a first setting region for setting a first component; asecond setting region for setting a second component; a free regionadjoining the first setting region; and a tube wall, wherein thickenedportions of the tube wall in the first and second setting regions havegreater thicknesses than a thickness of the tube wall in the freeregion, wherein the thickened portion of the tube wall in the firstsetting region extends into an interior of the support tube such that anouter diameter of the tube wall in the first setting region is the sameas an outer diameter of the tube wall in the free region.
 21. Thesupport tube of claim 20 wherein the first and second setting regionshave mutually different outer surfaces.
 22. The support tube of claim 20wherein an outer circumferential surface of the support tube is free ofany transition between the first setting region and the free region. 23.The support tube of claim 20 wherein an outer circumferential surface ofthe support tube is free of any offset between the first setting regionand the free region.
 24. The support tube of claim 20 wherein thethickened portion of the tube wall in the first setting region is 110%to 190% as thick as the thickness of the tube wall in the free region.25. The support tube of claim 20 wherein the tube wall is hydroformed.26. The support tube of claim 20 comprising the first component set onthe first setting region, wherein the first component is at least one ofa cam segment with at least two different cam tracks, or a slidingelement having at least one guide track.
 27. The support tube of claim20 wherein at least in the first setting region a material of the tubewall has on the outer circumferential surface at least one of a rolledformation or a longitudinal toothing.